The present invention relates to a clamp-type locking mechanism, as used, for example, in seat-height adjustments of motor vehicles.
Conventional locking mechanisms include a rotatable driven element which can be secured with respect to a holding element formed, for example, as housing by means of a releasable clamp connection in one, preferably in both, rotation directions. In case of a seat-height adjustment, a selected seat position can be implemented in this manner. An adjustment element is provided to release the clamp connection and to rotate the driven element with respect to the holding element. Thus, when incorporated in a seat adjustment, a rotation of the driven element results in a modification of the seat position.
A clamp-type locking mechanism is known, for example, from WO-A 96/20352, and includes a driven element which is rotatably received in a housing. Clamping ramps of the driven element and a cylindrical clamping track of the housing define clamping gaps for receiving spring-loaded clamp rollers. An adjustment element is swingable to a limited extent with respect to the driven element and engages between the driven element and the housing. The adjustment element includes engagement members which press the clamp rollers out of their clamping gaps in order to permit a rotation of the adjustment element in unison with the driven element. This clamp-type locking mechanism has furthermore a friction device for transmitting a friction moment between the housing and the driven element. This friction device prevents an undesired stick-slip effect by which the clamp rollers are clamped and released again in rapid sequence. This stick-slip effect may be caused by a torque applied on the driven element and acting in same direction as the adjusting moment introduced into the adjustment element. The friction device is formed here by a friction disk which is positively connected to the driven element and has an outer surface area which bears upon the cylindrical clamping track of the housing. This type of friction device suffers the drawback that the transmitted friction effect decreases as the wear of the friction surface progresses, so that the pressing action between the friction disk and the housing decreases with increasing material wear of the friction disk.